If Customer Purchased The 100mbps Probe And Later Wish To Upgrade To 1Gbps Probe Or Higher. What Is The Process For Them To Upgrade?

Customer will still need to purchase a new probe rated to 1Gbps, and to also upgrade the subscription to 1Gbps. 

Note that if the customer is already planning to migrate to a larger link then 1Gbps probe may be the best option for them in the first place.